1. Field of the Invention
The present invention relates to a semiconductor device, and particularly to a semiconductor device with a bonding pad electrode layer for inputting and outputting electrical signals to and from the external.
2. Description of the Background Art
In the processes for manufacturing semiconductor devices, a device referred to as a probe card has been conventionally used to inspect electrical characteristics of the semiconductor devices. FIG. 9 is a cross section illustrating a conventional probe card. The conventional probe card shown in FIG. 9 has an opening 114 formed approximately at the center of a substrate 113. Provided around opening 114 are a plurality of probe needles 115 of tungsten (W) towards the center of opening 114. Probe needle 115 is connected via a wiring to a terminal (not shown) arranged at a periphery of substrate 113. In inspection, the terminal is connected to an inspection device referred to as a prober.
The probe card is opposed to a surface of a semiconductor device subject to inspection and is arranged to allow the tip of probe needle 115 to come in contact with a bonding pad electrode formed on the surface of the semiconductor device. In inspecting electrical characteristics of the semiconductor device, probe needle 115 is brought into contact with the bonding pad electrode formed on the surface of the semiconductor device.
A description will now be provided as to how a probe needle comes into contact with a bonding pad electrode of a semiconductor device in the inspection.
FIG. 10 is a cross section of a bonding pad electrode of a conventional semiconductor device. The semiconductor device shown in FIG. 10 has a bonding pad electrode 102 of aluminum formed on a silicon substrate 101. An SiO.sub.2 -formed protection film 103 is formed to cover silicon substrate 101 and a portion of the upper surface and the side surface of bonding pad electrode 102. Formed on SiO.sub.2 -formed protection film 103 is a polyimide protection film 104. A contact hole 107 reaching bonding pad electrode 102 is formed in polyimide protection film 104 and SiO.sub.2 -formed protection film 103. On a surface of bonding pad electrode 102, aluminum is oxidized and aluminum oxide 106 is thus formed.
FIGS. 11 and 12 are schematic views for illustrating a contact between a probe needle and a bonding pad electrode of a semiconductor device subject to inspection in inspecting electrical characteristics of the semiconductor device. As shown in FIG. 11, when silicon substrate 101 (note that SiO.sub.2 -formed protection film 103 and polyimide protection film 104 shown in FIG. 10 are omitted in FIGS. 11 and 12) is raised, aluminum oxide 106 formed on a surface of bonding pad electrode 102 comes into contact with a tip 109 of a probe needle 108. Since aluminum oxide 106 is an insulator, a simple contact of tip 109 of the probe needle with aluminum oxide 106 does not result in electrical connection between tip 109 of the probe needle and bonding pad electrode 102.
Accordingly, silicon substrate 101 is further raised, as shown in FIG. 12. This allows the probe needle to be elastically deformed and tip 109 of the probe needle is moved in the horizontal direction. Thus, aluminum oxide 106 on the surface of bonding pad electrode 102 is exfoliated from the surface of bonding pad electrode 102 to allow direct contact between bonding pad electrode 102 and tip 109 of the probe needle so that the electrical characteristics of the semiconductor device can be inspected. Electrical characteristics of semiconductor devices can also be inspected in a similar procedure if bonding pad electrode 102 is formed of copper or tungsten.
When the aluminum oxide on the surface of bonding pad electrode 102 or the like is removed as described above, adhesion of the aluminum oxide to the tip of the probe needle or the like will increase contact resistance, which often results in an inaccurate measurement of electrical characteristics of the semiconductor device. Various approaches have been taken in order to solve this problem. For example, Japanese Patent Laying-Open No. 4-351968 and Japanese Utility Model Application No. 7-13364 (Registered Japanese Utility Model No. 3025108) proposed that a probe needle is formed of a material which is abrasion-resistant and to which less foreign matters adhere so that the probe needle has long life span and is less often subjected to unsatisfactory contacts, i.e., ensures electrical contact.
Japanese Patent Laying-Open Nos. 56-119377 and 7-244074 proposed that the tip of a probe needle to which foreign matters adhere is stuck several times into a resin parent material, such as an elastic silicon rubber mixed with a fines abrasive, such as whetstone, and the tip and side surface of the probe needle are thus scraped off to remove the aluminum oxide resulting in causing unsatisfactory contacts and thus achieve good electrical contact.
However, conventional methods of improving electrical contact are mainly related to probe card and probe needle, as described above, and it can be said that any approaches have hardly been made with respect to bonding pad electrode. Thus, conventional methods of improving electrical contact have not always sufficiently improved electrical contact. Furthermore, the conventional approaches have the disadvantage that the burden of maintenance of probe cards is increased.